Tracking and/or guidance systems

Abstract

A tracking and/or guidance system is disclosed for defining a route to be followed by a vehicle or projectile to a target. The system includes a tracking device which is arranged firstly to operate in an acquisition mode, applicable when the vehicle or projectile is close to the device, and subsequently to be progressively converted into a tracking mode as the distance between the vehicle or projectile and the device increases. In the acquisition mode, the device has a wide field of view but is relatively insensitive to deviations of said vehicle or projectile from said route. As the aforesaid distance increases, however, the field of view is progressively reduced and the sensitivity to said deviations is progressively increased. The invention thus provides a system which is suitable for the both initial acquisition and long range guidance of a vehicle or projectile aimed towards a distant target whilst using a conveniently small detector arrangement.

What I claim is: 
     
       1. A tracking and/or guidance system for defining a course to be followed by a vehicle or projectile aimed towards a target, including a tracking device having an acquisition mode, applicable when the vehicle or projectile is relatively close to the device and in which mode the device exhibits a relatively wide field of view but a relatively low discrimination with regard to deviations of said vehicle or projectile from said course, and means for progressively converting said device from operation in said acquistion made to operation in a tracking mode, in which it exhibits a relatively narrow field of view but a relatively high discrimination with regard to said deviations, as the distance between the vehicle or projectile and the device increases, the said device comprising: a. objective lens means adapted to receive radiant energy, from said vehicle or projectile,   b. field lens means arranged to receive radiant energy from said objective lens means and being disposed in the focal plane thereof,   c. detecting means having a surface sensitive to said radiant energy and adapted to receive radiant energy from said field lens means, the detecting means being arranged to produce electrical output signals indicative of said deviations, and   d. drive means operative on said detecting means and effective i. in said acquisition mode to space said detecting means from said field lens means by a predetermined distance so that said radiant energy received by said surface is diffused over a substantial part of said surface, and   ii. in response to, and concomitently with, increasing distance of said vehicle or projectile from said device to progressively reduce the spacing between said detecting means and said field lens means so that said radiant energy is focused with increasing sharpness on said surface as the distance between the vehicle or projectile and said device increases.     
     
     
       2. A system according to claim 1 wherein said device further includes the following elements disposed between said objective lens means and said field lens means: a. a concave mirror having a radius of curvature substantially equal to two-thirds of the focal length of said objective lens means and angled with respect to the optic axis thereof,   b. a further lens disposed to receive radiant energy reflected from said concave mirror and being spaced therefrom by a distance substantially equal to one half of the focal length of said objective lens means, and   c. a plane mirror located behind and parallel with said further lens and arranged to reflect said radiant energy back through said further lens and toward said field lens means.   
     
     
       3. A system according to claim 1 including means for utilising said electrical signals to modify the course of said vehicle or projectile. 
     
     
       4. A system according to claim 2 wherein said plane mirror comprises image stability mirror means arranged to reduce the effects of vibration on the system. 
     
     
       5. A system according to claim 2 including a diffusing means located in front of said field lens. 
     
     
       6. A system according to claim 5 wherein said diffusing means comprises a fibre optic plate. 
     
     
       7. A system according to claim 2 including aperture means, for limiting the aperture of said objective lens means, which comprises an iris the diameter of which is arranged to decrease during the time period through which the spacing between said detecting means and said field lens means is progressively reduced.